One.relative_identifier(
  1 <= 2,
  key: 3 <= 4
) <= Two.relative_identifier(
  2 <= 1,
  key: 4 <= 3
)
One.relative_identifier(
  1 <= 2,
  key: 3 <= 4
)(
  4 <= 5,
  key: 6 <= 7
) > Two.relative_identifier(
  2 <= 1,
  key: 4 <= 3
)(
  5 <= 4,
  key: 7 <= 6
)
One.relative_identifier key: 1 <= 2
One.relative_identifier unqualified 1 <= 2,
                                    key: 3 <= 4
One.relative_identifier 1 <= 2,
                        key: 3 <= 4